A distance indication can be obtained in the following manner. In a transmission step, an electromagnetic signal is transmitted towards an object whose distance needs to be determined. In a reception step, a reflection of the electromagnetic signal, which is caused by the object, is received with a given delay. The distance indication can be provided on the basis of this delay.
This principle, which is used in radar equipment, typically involves one or more antennas that have a given orientation and a given directional antenna pattern. The electromagnetic signal is transmitted in the form of the beam that has a particular direction. The orientation of the antenna and its directional antenna pattern determine the direction of the beam, which should point to the object whose distance needs to be determined.
The article entitled “Performance of obstacle detection and collision warning system for civil helicopters” by N. Yonemoto et al. published in the Proceedings of SPIE 6226, 622608 (2006), describes an obstacle detection and collision warning system for civil helicopters in which a color camera, an infrared camera and a Millimeter Wave (MMW) radar are employed as sensors. The MMW radar provides distance information. A personal computer (PC) is used as a data processor, which gathers color images, infrared images, and radar data to provide enhanced obstacle images on a display. Another PC controls the MMW radar and its scanning equipment, which comprises a gimbal ring. The sensors are mounted on the gimbal ring to manipulate the direction of the axis of the sensor or to eliminate helicopter vibration.